Man-made boards, such as fiberboard, e.g., hardboard; chipboard; oriented strand board-fiberboard composites; particle board; oriented strand board-particle board composites; and the like, commonly are embossed on their intended visible major surface in the manufacture of interior panelling, exterior siding, and particularly in the manufacture of door skins that are laminated to a support structure or frame, on both major surfaces, for replicating multi-panel doors having surfaces that are man made, rather than the very expensive natural wood "6-panel" doors. Commonly, such articles are molded from a planar cellulosic mat to include one or more interior or "closed" depressions, within an interior of the article, such as one or more square or rectangular depressions that do not extend to an outer edge of the article.
The cellulosic fibers or particles used to form the loose mat, e.g., a 2 inch thick layer of cellulosic fibers, initially may be bone dry after the fibers have been dried and felted, but the cellulosic materials in such mats absorb moisture from the atmosphere and generally include about 2% to about 10% moisture when molded via hot pressing, depending upon the humidity in the region where such mats are stored and/or manufactured. A molded or embossed design in a layer of cellulosic material that leaves interior depressions in the molded article is difficult to provide without surface defects because gases formed during hot-pressing, e.g., vaporized moisture, cannot escape from the mold cavity via venting to an exterior edge of the molded article when the molded article is hot-pressed to a constant mold level completely surrounding the formed interior depressions.
In some mold designs formed in wood composites, venting is accomplished by disposing a gas pervious material, e.g., a temperature-resistant, gas-pervious fabric, between a back half of the mold cavity and a non-visible side of the product being molded, to achieve controlled gas venting without blister formation in the molded article. Controlled gas venting during the hot-press molding of wood composite articles, however, tends to disrupt the complete consolidation and bonding of the molded articles along the molded edges, due to the escape of gas at the edges, causing excessive scrap or wasted material. Wasted material results from trimming the incompletely consolidated edges, containing valuable cellulosic material and binder, which must be trimmed away to achieve solid, completely consolidated, scratch resistant man-made board material over the entire major, exterior surface of the trimmed molded article. Accordingly, when such waste cannot be tolerated, a mechanical dam is included, surrounding the mold cavity, to eliminate essentially all gas venting during the hot-press molding step to avoid "punky" edges that end up as waste.
A typical mechanical mold dam is a metal border extending from, and perpendicular to, one half of the mold or die, and extending, for example, 0.030 inch vertically toward the other half of the mold or die, to create sufficient pressure on the material being molded, completely surrounding the mold cavity, to prevent essentially all gas escape until the mold cavity is opened. Gas venting, when such mechanical dams are used, occurs almost exclusively as a result of opening the mold cavity upon completion of the hot-press molding step. The sudden reduction in pressure upon mold cavity opening, however, sometimes causes a sudden release of water vapor trapped beneath the upper surface of the molded article, thereby causing a portion of the visible molded surface to bubble or blister--a portion of the molded surface delaminates from the remaining thickness because of the sudden escape of gas from an interior portion of the molded article. This blistering problem is most severe when attempting to mold detailed designs onto an inclined interior surface portion of closed depressions molded into wood composites.
Other problems occur in attempting to form the above-described inclined molded portions on an interior surface of closed depressions in a molded wood composite article, particularly when it is commercially necessary to paint such inclined surfaces to provide an aesthetically pleasing outer surface. One type of product, in particular, that must include excellent embossing detail and superior aesthetic qualities to be commercially acceptable, is a door skin that simulates a multi-panel natural wood door on both major faces of a support substrate or frame member. Door skins, or door faces, require detailed, inclined interior molded walls having a plurality of relatively close contours that include varied curves and planar surfaces. It has been found that these interior, inclined molded surfaces of interior inclined molded depression walls are very difficult to paint uniformly due to density differences, because of various curved and planar adjacent contours and due to the confined locations of the inclined surfaces within the relatively small, molded depressions. These angled or inclined surfaces on wall portions molded into depressions formed in the interior of the product are extremely difficult to provide with embossed surfaces representing, for example, a wood grain pattern, since such embossed texture on depression-interior inclined walls have a tendency to cause the article to stick to the mold cavity at the embossed inclined wall, causing fiber to pull away from the surface of the molded article when it is removed from the mold cavity.
Another problem common to the molded wood composite articles described above is in stacking a plurality of the molded articles for efficient shipping. Extant door skins, for example, when stacked one above another, having a depression profile as shown in the drawing identified as "Prior Art" have a tendency to damage, particularly in the upper decorative surface of the lowermost articles, due to abrasive contact on the detailed depression-interior inclined surfaces, particularly on the convex, uppermost "bead" of a "bead and cove" Colonist design, where aesthetics are most important, and where damage is most apparent.
The molded wood composite articles of the present invention solve some or all of the above-mentioned deficiencies in prior art molded wood composite articles to provide a molded wood composite article that has inclined, decorative depression-interior molded walls having upper, decorative inclined surfaces of relatively uniform density; can be painted with uniform paint hold-out; has molded, inclined surfaces that are accessible for buffability, in the preferred embodiment; and wherein the molded, inclined depression-interior surfaces are capable of being embossed with excellent texture or grain detail to provide an extremely aesthetic, detailed texture or grain design. In the preferred embodiment, the inclined depression-interior walls are longer and less severely inclined (about 25.degree. to about 38.degree.) than prior art depression-interior molded wall surfaces, and include a profile in the depression-interior, inclined molded surfaces such as an embossed "bead and cove" design, that permits excellent stacking of the articles for efficient, and essentially damage-free shipping and storage, while stacking more articles, one upon another.